The present invention relates to catalytic converters and in particular, to insulated catalytic converters having heating means, temperature control means and heat storage means.
When a cold internal combustion engine with a catalytic converter is started, the emission of pollutants is high, as the catalyst within the catalytic converter does not function at low temperatures. The exhaust emitted at start up heats the exhaust manifold and the exhaust pipe before heating the catalytic converter. It takes several minutes for the cold catalytic converter to be heated to “light off” temperature. The “light off” temperature is the temperature at which the catalytic converter oxidizes at least fifty percent of hydrocarbons in engine exhaust. It has been reported that 60 to 80 percent of all hydrocarbon emissions occur during the first few minutes after engine startup. To reduce the emission of pollutants at startup efforts have been directed at:
maintaining the catalytic converter at a functional temperature using fuel combustion,
preheating the catalytic converter,
rapidly heating the catalytic converter after startup using electrical heating, or a increased fuel air ratio, and
storing pollutants, in zeolites, until the catalytic converter has reached a functional temperature.
Efforts have also been made to control catalytic converter temperature during engine operation. Aspects of the technology for controlling catalytic converter temperature during engine operation are related to aspects of maintaining the catalytic converter at functional temperatures between engine uses.
1. Catalytic Converter Insulation and Air Flow Control Systems
Benson et al. in U.S. Pat. No. 5,477,676, dated Dec. 26, 1995, describes a catalytic converter surrounded by a variable conductance insulation for maintaining the operating temperature of the catalytic converter at a optimal temperature. The insulation “inhibits heat loss when raising the catalytic converter temperature to light off temperature”. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. This variable insulation is used to reduce the problem of overheating the catalyst which can lead to accelerated aging of the catalyst or even permanent damage to the catalytic converter. The variable conductance insulation system proposed is conceptually and mechanically complex, requiring numerous mechanical components and a complex manufacturing, assembly and installation.
Bainbridge in U.S. Pat. No. 5,163,289, dated Nov. 17, 1992, and in U.S. Pat. No. 5,092,122, dated Mar. 3, 1992, discloses a “insulation jacket around the exhaust pipe which is composed of fibers that conduct heat better at higher temperatures than at lower temperatures, and “allowing the exhaust pipe to reach the light off temperature of the catalytic converter in a short time”. The function of this refractory fiber insulation is based on fiber density and on the thickness of the blanket of fibers. The insulating refractory fibers are contained in a double walled flexible tube that is slid over a existing exhaust pipe. The walls of the flexible tube are made of corrugated stainless steel tubes.
Ingermann et al. in U.S. Pat. No. 5,331,810, dated Jul. 26, 1994, teaches an exhaust pipe with a low thermal capacitance inner pipe and a outer heavy gauge pipe. The thin pipe is supported in the center of the outer pipe such that an insulating air space exists between the two pipes. The outer pipe is not insulated. No effort is made to control air movements within the enclosed insulating air space. From this “the thin walled pipe”, “causes the heat energy in the combustion product's to reach the exhaust processor in a short period of time during the start up of a cold engine”. The problem of overheating of the catalytic converter, during extended engine operation, caused by insulating the exhaust pipe is not dealt with.
Rohrbaugh in U.S. Pat. No. 5,904,042 dated May 18, 1999, discloses “a diesel exhaust system that reduces harmful gases and particulate pollutants”, the system “includes at least one combination catalytic converter and particulate filter”. Rohrbaugh states “the catalytic converter is contained in a insulated canister which itself is contained in a shroud, for containing the heat generated by catalytic reactions. The insulation also serves to lower the outside temperature of the canister”. An axial fan blows air between the canister and shroud to reduce the exterior temperature of the shroud to a acceptable level. However, air flow is directed through the canister and not the catalytic converter. The purpose of the air flow is to cool the shroud while maintaining the heat of the catalytic converter.
Kizer and Borroni-Bird in U.S. Pat. No. 5,987,885 dated Nov. 23, 1999, and in U.S. Pat. No. 5,983,628 dated Nov. 16, 1999, describes a fan blown cooling system for blowing air around tubes which are part of a combination catalytic converter and heat exchanger unit. The heat exchanger “unit includes a plurality of spaced apart tubes” the “tubes include a substrate on which is formed a catalyst that reduces or eliminates harmful by products”. The speed of the fan is controlled variably to adjust the temperature of exhaust emissions in response to various output data”, “two or more catalysts that have different operating ranges” can be used. The tubes may be electrically heated to extend the duration whereby the catalytic converter is operating within its efficient conversion window.
Yamada et al. in U.S. Pat. No. 3,947,544 dated Mar. 30, 1976 describes an exhaust pipe upstream of the catalyst provided with a double wall conduit. Secondary air is continuously passed through the outer conduit and selectively directed into the catalyst bed or vented to the atmosphere depending upon temperature conditions in the catalyst bed. The primary objective of Yamada and Kitamura is “avoiding over heating and thermal destruction of the catalyst bed” while insulating the exhaust pipe upstream of the catalytic converter.
Yuge et al. in U.S. Pat. No. 3,910,042 dated Oct. 7, 1975, describe using a “blower to be driven so that air is forced into and flows through the second group of passages”, a heat exchanger within a catalytic converter, to thereby prevent the catalyst from being melted. Also disclosed is a heat source such that the air supplied to the bed is heated to heat the bed to a temperature at which the catalyst is appropriately activated. A forced air circulation through a combined catalytic converter heat exchanger is used to control catalytic converter temperature. However, heating of air electrically, then passing the air through the catalytic converter is inefficient and results in a loss of energy. More energy is required to heat the increased mass of a catalytic converter combined with a heat exchanger. This increased energy requirement slows the temperature increase of the catalytic converter at start up leading to higher emissions. This comment also applies to the exhaust pipe heat exchanger and the catalytic converter heat exchanger described by Kizer et al.
Kinnear et al. in U.S. Pat. No. 5,155,995 dated Oct. 20, 1992, describes an electrically energized heater in association with a catalytic converter. Kinnear et al. also describes pre-heating which is triggered by a mobile transmitter and a “functional verification device”. Also described is a catalytic converter which is a unit comprising a outer casing which surrounds, but is spaced from, an inner canister. The gap forms a thermal barrier and can be filled with a thermal resistant or insulating material such as asbestos or glass fiber. No solution is given for the problem of catalytic converter over heating and loss of function that results when a catalytic converter is insulated
Onoda et al. in U.S. Pat. No. 3,747,346 dated Jul. 24, 1973 describes a “encasing structure disposed about the exhaust pipe upstream of the catalytic converter and spaced from the exhaust pipe. This gap functions to prevent heat loss from the exhaust pipe and which permits the air to pass there through to prevent an excessive high temperature of the exhaust pipe”. Further “the walls of the encasing structure may be insulated with fibers or foam insulation, if desired”. Also “the encasing structure has an air inlet passage found at its upstream side and air outlet passage found at its downstream side”. The air inlet and outlet have “mechanically connected”, “valves”. These valves are controlled by a system receiving information from a temperature sensor that “detects the temperature of the catalyst”. This air flow control system reduces heat losses from the exhaust pipe heating the catalytic converter more rapidly to a operating temperature at startup. By allowing increased air flow around the exhaust pipe during engine operation the risk of over heating the catalytic converter is reduced.
Yamashita et al. in U.S. Pat. No. 5,845,486 dated Dec. 8, 1998, discloses an exhaust damper for opening and closing an exhaust pipe which is disposed downstream of a catalyst. The closed exhaust damper keeps the warmth of the catalyst. The invention described here has insulated flaps that open in the direction of the exhaust stream. There are two flaps in tandem in front of, and behind, the catalytic converter. The space between the two flaps being a air insulating space. The flaps are made of either a low thermal conductance ceramic, or thin vacuum panels. The flow of exhaust from the engine moves the flaps to a horizontal position opening the exhaust pipe. When the engine is turned off the flaps move to a vertical position where they block air movement in the exhaust pipe.
2. Heating of the Catalytic Converter
There are many prior art disclosures of electrically heated catalytic converters. None, however, adequately deal with the large amount of power needed to heat a converter to its light off temperature from ambient temperature and the problem of overheating if the converter is insulated. As well, electrical heating can heat catalytic converters too rapidly which may damage the catalyst. Rapid heating will cause natural deterioration of the catalyst over time.
Tandem catalytic converter inventions are also known and usually have a small catalytic converter positioned near the engine so that they are heated more rapidly than the main catalytic converter, which is positioned well away from the engine to prevent overheating, as is conventional practice. Tandem catalytic converter systems protect the main catalytic converter from over heating. The small catalytic converter near the engine is subjected to rapid heating and temperatures which can result in damage and loss of catalytic converter function. The strategy of tandem catalytic converter proposals appears to be to sacrifice the small catalytic converter at regular invervals. The servicing costs, and time loss related to the vehicle being in for service likely exceed the cost to the consumer of replacing the main catalytic converter. The degradation of the small catalytic converter is the general problem associated with tandem catalytic converter proposals.
Inventions using side-by-side catalytic converters have a small catalytic converter next to a large main catalytic converter. The small catalytic converter receives the exhaust at engine start-up and is rapidly heated to a operational temperature. After a initial period the exhaust is diverted to the main catalytic converter. Side-by-side catalytic converters do not reduce emissions. The main catalytic converter still has to be heated to a operating temperature by the passage of exhaust through it. While the small and main catalytic converters are being heated the exhaust is not treated and pollution emissions are high. Proposals based on a side by side catalytic converter system may reduce the level of pollutants emitted during the initial period, but extend cold start emissions over a longer time period. Since two exhaust pipes need to be heated the emissions of side by side catalytic converter proposals may actually be higher than if a a small catalytic converter were not used.
3. Fuel Combustion Heating
Mondt in U.S. Pat. No. 3,911,675 dated Oct. 14, 1975, describes “a converter heating system to maintain the catalytic converter at a predetermined temperature so that it is effective upon engine start-up to diminish products of combustion. The converter heating system includes in combination a small pump which draws a air fuel mixture from the fuel tank, a igniter and a pilot burner”. Mondt states “the present invention provides continuous heating means which maintain the catalytic bed temperature” and “includes a pilot burner for heating”. The invention of Mondt has a “housing formed preferably of a high chromium stainless steel”, no mention is made of the use of insulation to reduce heating requirements. Fuel burning systems require many parts which can break down, and safety concerns exist regarding having a combustion process operating without supervision. A fuel burning system cannot operate when a vehicle is parked within an enclosed area, a problem not addressed by Mondt.